Gas phase olefin polymerization with single site catalysts has been a well established art field since the invention of metallocene catalysts over two decades ago. Although, single site catalysts (such as metallocene catalysts, constrained geometry catalysts, and phosphinimine catalysts) are often chosen for their very high activity, the use of such catalysts can lead to reactor fouling especially in a fluidized bed gas phase reactor. Such fouling may include polymer agglomeration, sheeting, or chunking and may ultimately require reactor shut down.
In order to improve reactor continuity, several specialized catalyst preparative methods, operating conditions and additives (e.g. so called “continuity additives”) have been used to modify the performance of metallocenes (and other single site catalysts) and to reduce reactor fouling. For example, European Pat. Appl. No. 630,910 discusses reversibly reducing the activity of a metallocene catalyst using a Lewis base compound. Related methods employ long chain substituted alkanolamine and long chain substituted alkanolamide compounds to reduce the amount of reactor fouling in fluidized bed polymerizations processes. The use of substituted alkanolamines in combination with metallocene catalysts to improve reactor operability and reduce static levels is described in European Pat. No. 811,638 and U.S. Pat. Nos. 5,712,352; 6,201,076; 6,476,165; 6,180,729; 6,977,283; 6,114,479; 6,140,432; 6,124,230; 6,117,955; 5,763,543; and 6,180,736. The use of a substituted alkanolamide as a reactor continuity additive in metallocene catalyzed polymerization of olefins is described in Japanese Patent Abstract No. 2000-313717. Alkanolamines have been added to a metallocene catalyst prior to addition to a reaction zone (see U.S. Pat. Nos. 6,140,432; 6,124,230; 6,114,479) and they have been added directly to a reactor or other associated parts of a fluidized bed reactor processes such as the recycle stream loop (see European Pat. No. 811,638 and U.S. Pat. No. 6,180,729 respectively).
The literature also provides additive mixtures which provide enhanced reactor operability. Oil soluble sulfonic acid compounds, for example, are most often used in combination with a polysulfone copolymer and a polymeric amine to provide a mixture which is effective in reducing reactor static levels and reactor fouling (see U.S. Pat. Nos. 7,476,715; 6,562,924; 5,026,795, and 7,652,109). WO 2009/023111A1 teaches that treatment of an antistatic agent with an organometallic scavenger, prior to its entry into a polymerization zone, provides for high catalyst activity and reduced reactor fouling. U.S. Pat. No. 6,891,002 shows that using an aliphatic amide in combination with polyoxyalkylene glycol and a liquid hydrocarbon provides improved catalyst activity and low associated reactor fouling.
Despite these advances, there remains a need for new continuity additive packages which are economical, easy to use and provide the dual features: improved reactor operability and high catalyst activity.
We now report that a cocktail comprising fatty acid alkanolamides, an oil soluble sulfonic acid, and a dialkanolamine shows good ability to enhance reactor operability in the gas phase when used in combination with a single site polymerization catalyst. We note that the use of a related cocktail was disclosed in U.S. Pat. No. 7,638,585 in the context of improving the performance of Ziegler-Natta polymerization catalysts. The patent does not teach the use of single site catalysts. The continuity additives of the present invention also give higher catalyst activity at increased levels than a more traditional single component antistat, the substituted alkanolamine antistat compound, Atmer-163™.